This application is based on and claims priority under 35 U.S.C. xc2xa7119 with respect to Japanese Application No. 2000-342314 filed on Nov. 9, 2000, the entire content of which is incorporated herein by reference.
The present invention generally relates to a vehicle bumper. More particularly, the present invention pertains to a bumper reinforcement structure in a vehicle bumper device for absorbing collision impact or energy upon the occurrence of a vehicle collision.
An example of a known bumper device is disclosed in Japanese Patent Laid-Open Publication No. Hei.10(1998)-175485. This bumper device is positioned at the front and/or rear end of the vehicle body and includes a bumper reinforcement element secured to a side member of the vehicle body, an absorber member formed of an elastic material such as urethane and provided at the front region of the bumper reinforcement element, and a bumper cover member covering both the bumper reinforcement element and the absorber member.
As shown in FIGS. 9(a), 9(b) and 9(c), the bumper reinforcement element extends in the lateral direction of the vehicle and possesses a cross-section having a  shape when viewed in the lateral direction of the vehicle. The cross-sectional shape defines a rectangular outer profile with a crossing member dividing the cross-section in half. In light of space restrictions and improvements in the appearance of the vehicle body, the opposite ends of the bumper reinforcement element are curved so as to be accommodated in the bumper cover. This bumper reinforcement element is intended to absorb the collision impact upon the occurrence of a low speed vehicle collision to thus prevent damage or breakage of the vehicle body.
The material that is widely used to form the bumper reinforcement element is typically an aluminum alloy extruded material or a roll-formed steel (especially high tension steel). This material makes it possible to form the bumper reinforcement element into the cross-section noted above which is superior in collision impact absorption.
Recent developments in vehicle body appearance design have resulted in a narrowing of the space in which the bumper reinforcement element is to be accommodated. Thus, to mount the known bumper reinforcement element while maintaining the required impact absorption capability, it is necessary to make the shape of the bumper reinforcement element more complex. This requires relatively precise bending such as small-radius bending or complex bending, which involves a more complex production process and bending machine.
In addition, to reduce the likelihood of vehicle damage and passenger injury, while also lessening repair cost, the bumper reinforcement element should possess rather superior collision impact absorption capability. To address such a requirement, the bumper reinforcement element can be redesigned so that it is able to withstand higher loads. This can be achieved by, for example, forming file bumper reinforcement element with additional inner walls or with increased wall thickness. However, this undesirably increases the mass of the bumper reinforcement. In addition, the side member of the vehicle body to which the resulting bumper reinforcement element is secured has to be reinforced so as not to be deformed.
To address the foregoing problems, the aforementioned Japanese Patent Laid-Open Publication No. Hei.10(1998)-81182 proposes providing another separate impact absorption element at the bumper reinforcement element. However, such a proposal requires an additional production process for mounting the additional impact absorption element, thus resulting in an inevitable cost increase.
A need thus exists for a bumper reinforcement element that is able to address the aforementioned difficulties.
It would be desirable to provide a bumper reinforcement element that possesses a shape capable of being relatively easily formed, yet which is capable of fulfilling its function in a narrowed space as a result of the vehicle body appearance, which is able to absorb collision impacts in a lower load deformation region in which the side member fails to deform, and which is capable of being mass produced at a relatively low cost.
According to one aspect of the invention, a bumper reinforcement structure includes a bumper reinforcement element positioned at the front end and/or rear end of a vehicle body and fixed to a side member of the vehicle body. The bumper reinforcement element has a closed hollow cross-section and extends in the vehicular lateral direction. The bumper reinforcement element is formed of any one of a light alloy and a steel. A concave or convex portion is formed on at least one surface of the bumper reinforcement element to change the shape of the cross-section of the bumper reinforcement element along the vehicle lateral direction.
The bumper reinforcement structure of the present invention can be formed relatively easily even though the bumper reinforcement structure has a shape which performs its intended function when positioned in a narrowed space so as to make possible the desired vehicle body appearance.
Preferably, the concave portion or convex portion progressively changes in depth, width, and/or shape to change the shape of the cross-section of the bumper reinforcement element in the vehicle lateral direction. With such a construction, the load, which fails to deform the side member, does not change rapidly, thus making it possible to absorb the required collision impact or energy amount effectively.
The concave portion or convex portion can be formed at the vehicle lateral inner portion of the vehicular chassis or body side of the bumper reinforcement.
According to another aspect of the invention, a bumper reinforcement structure includes a bumper reinforcement element positioned at least at the front end or rear end of the vehicle body. The bumper reinforcement element has a portion fixed to a side member of the vehicle body, with such portion having an upper surface and a lower surface. At least one of the upper surface and the lower surface is formed with a bead portion which is at least either concave or convex and which extends in a direction transverse to the vehicle lateral direction. Such a structure increases the rigidity of the bumper reinforcement structure by not increasing the wall thickness of the bumper reinforcement element, thus making it possible to obtain a load vs. deformation amount curve possessing superior collision impact absorption attributes.